Volumetric metering pump

ABSTRACT

A volumetric metering pump for accurately dosing small quantities of liquid, in which two interconnected identical parttoroidal pistons are arranged in separate cylinders. Small pulse jerks are simultaneously applied to each piston by a rockable member connected to a step-by-step electric motor, so that one piston draws liquid into its cylinder while the other piston expels liquid from its cylinder. This pistons are thus caused to move along arcuate strokes in the direction of their respective axes. A slide valve is provided firstly to direct liquid from an inlet duct to one cylinder and to an outlet duct from the other cylinder. At the end of each stroke this situation is reversed.

United States Patent Commarmot [15] 3,653,787 1 Apr. 4, 1972 Roger Commarmot, Lyon, France [30] Foreign Application Priority Data Oct. 23, 1969 France ..6936425 [52] U.S. Cl ..417/4l5,4l7/531 [51] Int. Cl ..F04b 35/04, F04b 21/02, F04b 39/10,

' F04!) 17/00 [58] FieldofSearch ..417/415,52l,53l

[56] References Cited UNITED STATES PATENTS 1,801,419 4119,31VMIEUIELUITITTZ 2,930,915 3/1960 Reutter ..4l7/4l5X Primary Examiner-Robert M. Walker AttorneyCushman, Darby & Cushman 57 ABSTRACT A volumetric metering pump for accurately dosing small quantities of liquid, in which two interconnected identical part-toroidal pistons are arranged in separate cylinders. Small pulse jerks are simultaneously applied to each piston by a rockable member connected to a step-by-step electric motor so that one piston draws liquid into its cylinder while the other piston expels liquid from its cylinder. This pistons are thus caused to move along arcuate strokes in the direction of their respective axes. A slide valve is provided firstly to direct liquid from an inlet duct to one cylinder and to an outlet duct from the other cylinder. At the end of each stroke this situation is reversed.

8 Claims, 3 Drawing Figures VOLUMETRIC METERING PUMP The present invention relates to volumetric metering pumps.

It has already been proposed to provide a volumetric metering pump intended for the continuous delivery of very small flow rates of liquid with a very high standard of precision.

This pump comprises two pistons mounted in opposition which are each displaced within a separate cylinder the ends of which are connected by way of a distributing slide valve respectively to suction and delivery conduits, each piston being secured to a common driving device imparting identical movements to it by successive impulses. A device periodically and simultaneously changes the direction of movement of each piston and also the position of the distributing slide valve, this double changing being carried out in the interval of time between two successive impulses without modifying the duration of this interval.

This pump comprises pump bodies and cylindrical pistons in accordance with the usual rules of mechanical construction. The control of the pump is effected from a mechanical impulse generator such as an electric motor rotating through a specific angle at each impulse (called a step-by-step motor").

The construction of a pump of this kind requires the use of several mechanical members which co-operate to transform the alternate rotational movements of the electric motor into alternate translational movements and transmit these to the pistons. These members are essentially constituted by a pinion mounted on a shaft guided by two bearings and by a rack moving by means of a ball slide in a slideway. These members have a relatively considerable bulk and the very high performances required of the pump impose strict tolerances as regards their construction and assembly. It has been found that such demands were often not necessary, and that often a pump of much smaller bulk was needed.

According to the invention there is provided a volumetric metering pump for accurately dosing very small quantities of liquid, such pump comprising first and second cylinders, first and second identical interconnected part-toroidal pistons in said first and second cylinders respectively, first and second conduits connected to said first and second cylinders respectively to lead liquid to be pumped to and from said cylinders, an inlet and an outlet duct connected to said first and second conduits by a valve, means to move the valve between a first and a second position whereby when said valve is in the first position the inlet duct is connected to the first conduit and the outlet duct to the second conduit, and when the valve is in the second position, the inlet duct is connected to the second conduit and the outlet duct is connected to the first conduit, means to move the first and second pistons alternately in two arcuate strokes simultaneously along their respective part-circular axes and equally in a series of pulsed jerks, firstly in a direction to draw liquid doses into the first cylinder and expel liquid doses from the second cylinder, when the valve is in the first position, and subsequently at the end of a stroke of the pistons, to move the latter in the opposite direction, to draw liquid doses into the second cylinder and expel the liquid doses from the first cylinder, when the valve is in the second position, and means to reverse the operation of the valve moving means and the piston moving means .at the end of each stroke in the interval of time between two consecutive pulses.

In a preferred construction the pump comprises first and second cylinders, first and second part-toroidal pistons reciprocable in said first and second cylinders respectively, a rockable member carrying said pistons, a step-by-step reversing motor for rockably reciprocating said rockable member to move said pistons along their axes in a series of pulsed jerks, a fixed valving member, a valving movable with respect thereto between first and second pumping positions, a pair of solenoids for moving the movable valving member between its first and second positions, a liquid inlet and outlet to the valve assembly formed by the fixed and movable valving members, a pair of conduits connecting each cylinder separately to the valve assembly, passages in the valve assembly connecting the inlet to one of the conduits and the outlet to the other conduit when the movable valving member is in the first pumping position and connecting the outlet to said one conduit and the inlet to said other conduit when the movable valving member is in the second pumping position, a pulse generator to operate the motor in equal pulsed jerks, a pair of limit switches one at each end of the travel of the rockable member, and operated by the rockable member to actuate said solenoids to move the valving member from one of its pumping positions to the other, and to reverse the direction of operation of the motor at the end of each stroke of the pistons and delay means to ensure that the limit switches can only operate in the interval between two consecutive jerks.

In order that the invention will be better understood, the following description is given, merely by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is an elevational view of one embodiment of pump according to the invention;

FIG. 2 is a section taken on the line IIII of FIG. 1; and

FIG. 3 is a section on the line Illlll of FIG.- 1.

The pump comprises a step-by step motor 1, a frame 2, identical opposed pistons 3 and 4 of part-toroidal shape displaceable within cylinders 5 and 6.

Pistons 3 and 4 are mounted on a rockable member 7, fixed by a screw 9 to the shaft 8 of the motor 1. Thus the pistons 3 and 4 may be driven directly in two arcuate strokes along their respective axes. The member 7 describes a sector of a circle whose amplitude is limited by two abutments 20 and 19 each I provided with a limit switch 10 and 11.

The pistons are identical and are in the form of torus sections. The length of the pistons is generally between a half and a twentieth of the torus circumference length, and is preferably comprised between a half and a quarter of this circumference. The corresponding torus diameter is not critical; it is determined in accordance with the permissible bulk and the constructional possibilities for the'various parts constituting the pump. The length/diameter ratio of the pistons is comprised between 2 and 100.

The pump bodies or cylinders 5 and 6 do not have to be given a particular form, and it suffices for the pistons to travel therein freely in the direction of their axes. They are open at the end through which the piston extends and are provided at this end with a sealing element arranged about the piston. They are each provided with a conduit 12 and 13 connected to the fixed valve member 51 of the distributing slide valve 50 to be described later. They may be fixed to the frame 2 by any known means, for example collars l4 and 15.

The frame 2 also carries a valve assembly 50 together with its associated parts, as illustrated in greater detail in FIG. 3.

As can be seen in this Figure, the valve assembly 50 comprises a fixed valve member 51 and a movable member 52 urged against the fixed valve member 51 by a spring 24. The movable valve member 52 is provided with passageways 58 and 59 which are connected to an inlet duct 53 and an outlet duct 54. Similarly, the fixed valve member 51, which is bolted to a sub-frame 28 mounted on the frame 2, is provided with three passageways, 60, 61 and 62, the passageways 60 and 62 being connected in the form of a U." The passageway 61 is connected to a first conduit 13 and thence to the cylinder 6, while the conduits 60 and 62 are connected to a second conduit 12 and thence to the cylinder 5.

lnterposed between the fixed and movable valve members is a gasket 57 provided with passageways aligned with those of the fixed member 51.

In the drawings, the valve member 52 is illustrated in an intermediate position. In fact it is movable between a first position which is to the left of this intermediate position by a solenoid 29, operating the valve by means of the connecting rod 23 mounted in the bearing 26. Similarly a solenoid 30 is provided to move the valve member 52 to the right to a second position, through the intermediary of a connecting rod 25 mounted in a bearing 27.

The displacement of the movable valve member 52 is limited by abutment of two end members 31 and 32 against bearings 26 and 27, so that the passageways 58 and 59 are accurately aligned either with the passageways 60 and 61, or with the passageways 61 and 62.

The pump illustrated (FIGS. 1 and 2) is constituted by two pistons arranged end to end and adapted to be displaced in one and the same plane in accordance with a circumference coaxial with the axis of the motor. The pistons 3 and 4 are driven simultaneously in the same direction by the rockable member 7; they may be made in one piece.

It is advantageous to prevent any radial stress on the sealing elements arranged about the pistons. For this purpose the pump bodies can be mounted so that they can have free play if a piston force acts on them. Thus, for the toroidal pump bodies, it is advantageous to hold them towards their end by collars adapted to rotate about the diameter corresponding to their fixing point to the frame and to support the pump body simply at the height of the sealing element by spring blades l6, 17 the plane of which is tangential to the axis of the torus in this region and which are fixed to the frame 2 at their opposite end by means of a fixed support 18, these spring blades being apertured so as to allow the free passage of the member 7.

As a variant, it is possible to propose a pump provided with two pistons adapted to be displaced simultaneously in parallel planes on circumferences centered on the axis of the motor. This arrangement makes it possible to use pistons whose length may reach substantially a semicircumference. It is also possible to control the pump by a motor driving a ratchet wheel device or by any other device for generating and regulating mechanical impulses.

In operation of the above described apparatus, the inlet duct 53 is connected to a suitable source of liquid, and the outlet duct 54 to a location at which doses are to be dispensed. The motor 1 in this construction consists of a step-by-step electric motor, which rotates through a predetermined angle under the action of an electronic pulse supplied by an electronic device of known type (not shown). Such a mechanical pulse generator also serves as a mechanical pulse regulator, because if the successive angles through which it turns have not an absolutely identical value, the differences observed do not add together, and the errors introduced are not cumulative.

This mechanical pulse generating device rotates alternately in one direction and in the opposite direction, the changeover of the direction of rotation being successively brought about by each of the two switches and 11. Thus, when the motor 1 is rotating in one direction, the shaft 8 and member 7 are caused to move around in a jerky fashion, thus moving the pistons 3 and 4 in an 'arcuate stroke along their respective axes again in a jerky manner. Assuming that these members are all moving to the left'as viewed in FIG. 1, the piston 4 is moved to force liquid out through the conduit 48 to the valve assembly 50.

The electrical connection between the switches 10 and 11 and the solenoids 29 and 30, via an electrical control switching arrangement 69, is such as to ensure that the valve is in the first position, having been moved by the solenoid 29. With this arrangement, liquid as indicated above is forced through the conduit 13 into the passageway 61 and thence into the passageway 59 and leaves via the outlet duct 54. At the same time, the piston 3 moves to the left in the cylinder 5 and draws liquid in via the inlet duct 53, the passageway 58, the passageway 60 and the conduit 12. The pulses are of substantially equal length and duration.

The member 7 and its associated parts continue to move to the left until the member 7 strikes the limit switch 11. Suitable delay is arranged so that the switch is only effective in the space between two pulses. When the switch operates, it sends a signal via switching arrangement 69 to cause the motor to reverse its direction of rotation and also to de-energize the solenoid 29 and energize the solenoid 30. The member 7 then moves to the right in pulses and the reverse situation takes place, liquid being expelled from the cylinder 5 and drawn in the cylinder 6. Again reversal will take place when the member 7 operates the microswitch 10.

There may with advantage be provided in association with the mechanical-pulse generator, a mechanical, electromechanical or electronic speed-varying device for adjust- 4 ing at will the time between two successive pulses. A speedvarying device permits of readily adjusting a dose to the desired value and of covering a wide range of doses.

If it is desired to manipulate liquids which are incompatible with the nature of the material constituting the pump body and the piston, it is possible to interpose a diaphragm separator between each pump body and the conduit which connects it to the distributor, and to fill the portion of the apparatus concerning the pump with inert liquid such as water whereas the other portion of the apparatus is traversed by the liquid to be pumped.

The pump according to the invention affords the advantage of a simple construction, the pistons being the only portions requiring finishing with high tolerances.

EXAMPLE A pump is constructed as shown in the Figures. The metal parts in contact with the liquid are made of stainless steel (nickel, chromium, molybdenum 18/8/2). The pump bodies 5 and 6 are constituted by tubes having an internal diameter of 4 mm, a length of 70 mm, curved along arcs of a circle having a diameter of 68 mm. They are provided at their open end with a sealing ring constituted by a copolymer of vinylidene fluoride and hexafluoropropylene, which provides sealing tightness about the pistons. The pistons are constituted by a part the form of which is a section of a torus of 2.5 mm diameter and 2 X 55 mm useful length. Their surface is defined within tolerance of 4 u. The pistons are held by the rockable member 7 securely on the shaft of the impulse generator, constituted by an electrical step-by-step motor.'This motor is capable of effecting the revolution per 200 steps. Each step of the motor, therefore, communicates to the pistons an impulse which displaces them in rotational movement through an angle of l.8.

The travel of the pistons is regulated to a value of 50 impulses. The end-of-travel switches 10 and 11 actuate, in a time less than 0.1 second, the reversal of the direction of rotation of the step-by-step motor, as well as the displacement of the distributing slide valve.

A regular delivery of pulsed liquid is obtained with very great precision. This pump can be used in laboratory work, more particularly for chromatography.

We claim:

1. A volumetric metering pump for accurately dosing very small quantities of liquid, said pump comprising, in combination:

a. first and second cylinders;

b. first and second identical interconnected part-toroidal pistons in said first and second cylinders respectively, and having part-circular axes;

c. first and second conduit means connected to said first and second cylinders respectively, effective to lead liquid to be pumped to and from said cylinders;

d. an inlet duct and an outlet duct;

e. valve means connected to said inlet duct and said outlet duct and to said first and second conduit means;

f. means for moving said valve means between a first position, in which said inlet duct is connected to said first conduit means, and said outlet duct is connected to said second conduit means, and a second position in which said inlet duct is connected to said second conduit means, and said outlet duct is connected to said first conduit means;

g. means to move said first and second pistons alternately in two arcuate strokes simultaneously and equally in pulsed jerks along their respective axes, firstly in a direction effective to draw liquid doses into said first cylinder and expel liquid doses from said second cylinder, when said valve is in said first position, and subsequently, at the end of the stroke of said pistons, to move said pistons in the opposite direction, effective to draw liquid doses into said second cylinder and expel liquid doses from said first cylinder, when said valve is in said second position; and

h. means to reverse the operation of said valve moving means and said piston moving means at the end of each stroke in the interval of time between two consecutive pulses.

2. A pump as claimed in claim 1, wherein said valve means is a slide valve, comprising a fixed member and a movable member formed with passageways therein, said passageways in said movable member being connected to said inlet and outlet ducts, and said passageways in said fixed member being connected to said first and second conduit means.

3. A pump as claimed in claim 2, wherein said valve moving means comprises a first solenoid, to move said movable member to said first position, and a second solenoid to move said movable member to said second position.

4. A pump as claimed in claim 3, wherein said reversing means comprise switch means connected to said solenoid, and operated by said piston moving means.

5. A pump as claimed in claim 1, wherein said part-circular axes form parts of the same circle.

6. A pump as claimed in claim 1, wherein said part-circular axes are parallel and coaxial to one another.

7. A pump as claimed in claim 1, wherein the means to move the two pistons simultaneously in pulsed jerks comprise an electrical step-by-step motor.

8. A volumetric liquid metering pump to deliver with very high precision limited quantities of liquid, said pump comprising in combination:

a. first and second cylinders;

b. first and second identical part-toroidal pistons reciprocable in said first and second cylinders respectively;

c. a rockable member carrying said pistons;

d. a step-by-step reversing motor operatively connected to rockably reciprocate said rockable member effective to move said piston along their axes in jerks;

e. a fixed valving member;

f. a valving member movable with respect to said fixed valving member between first and second pumping positions and forming with'said fixed valving member a valve assembly;

g. a pair of solenoids effective to move said movable valving member between said first and second pumping positions;

h. a pair of conduit means connecting each cylinder separately to said valve assembly;

i. liquid inlet means and liquid outlet means connected to said valve assembly;

j. passage means in said valve assembly connecting said inlet means to one of said conduit means and said outlet means to the other of said conduit means when said movable valving member is in said first pumping position, and connecting said outlet means to said one conduit means and said inlet means to said other conduit means when said movable valving member is in said second pumping position;

k. a pulse generator effective to operate said motor in equal pulsed jerks;

l. a pair of limit switches, one at each end of the travel of said rockable member, and operated by said rockable member effective to actuate said solenoids to move said valving member from one of its pumping positions to the other, and effective to reverse the direction of operation of said motor, at the end of each stroke of said pistons;

and m. delay means effective to insure that said limit switches 

1. A volumetric metering pump for accurately dosing very small quantities of liquid, said pump comprising, in combination: a. first and second cylinders; b. first and second identical interconnected part-toroidal pistons in said first and second cylinders respectively, and having part-circular axes; c. first and second conduit means connected to said first and second cylinders respectively, effective to lead liquid to be pumped to and from said cylinders; d. an inlet duct and an outlet duct; e. valve means connected to said inlet duct and said outlet duct and to said first and second conduit means; f. means for moving said valve means between a first position, in which said inlet duct is connected to said first conduit means, and said outlet duct is connected to said second conduit means, and a second position in which said inlet duct is connected to said second conduit means, and said outlet duct is connected to said first conduit means; g. means to move said first and second pistons alternately in two arcuate strokes simultaneously and equally in pulsed jerks along their respective axes, firstly in a direction effective to draw liquid doses into said first cylinder and expel liquid doses from said second cylinder, when said valve is in said first position, and subsequently, at the end of the stroke of said pistons, to move said pistons in the opposite direction, effective to draw liquid doses into said second cylinder and expel liquid doses from said first cylinder, when said valve is in said second position; and h. means to reverse the operation of said valve moving means and said piston moving means at the end of each stroke in the interval of time between two consecutive pulses.
 2. A pump as claimed in claim 1, wherein said valve means is a slide valve, comprising a fixed member and a movable member formed with passageways therein, said passageways in said movable member being connected to said inlet and outlet ducts, and said passageways in said fixed member being connected to said first and second conduit means.
 3. A pump as claimed in claim 2, wherein said valve moving means comprises a first solenoid, to move said movable member to said first position, and a second solenoid to move said movable member to said second position.
 4. A pump as claimed in claim 3, wherein said reversing means comprise switch means connected to said solenoid, and operated by said piston moving means.
 5. A pump as claimed in claim 1, wherein said part-circular axes form parts of the same circle.
 6. A pump as claimed in claim 1, wherein said part-circular axes are parallel and coaxial to one another.
 7. A pump as claimed in claim 1, wherein the means to move the two pistons simultaneously in pulsed jerks comprise an electrical step-by-step motor.
 8. A volumetric liquid metering pump to deliver with very high precision limited quantities of liquid, said pump comprising in combination: a. first and second cylinders; b. first and second identical part-toroidal pistons reciprocable in said first and second cylinders respectively; c. a rockable member carrying said pistons; d. a step-by-step reversing motor operatively connected to rockably reciprocate said rockable member effective to move said piston along their axes in jerks; e. a fixed valving member; f. a valving member movable with respect to said fixed valving member between first and second pumping positions and forming with said fixed valving member a valve aSsembly; g. a pair of solenoids effective to move said movable valving member between said first and second pumping positions; h. a pair of conduit means connecting each cylinder separately to said valve assembly; i. liquid inlet means and liquid outlet means connected to said valve assembly; j. passage means in said valve assembly connecting said inlet means to one of said conduit means and said outlet means to the other of said conduit means when said movable valving member is in said first pumping position, and connecting said outlet means to said one conduit means and said inlet means to said other conduit means when said movable valving member is in said second pumping position; k. a pulse generator effective to operate said motor in equal pulsed jerks; l. a pair of limit switches, one at each end of the travel of said rockable member, and operated by said rockable member effective to actuate said solenoids to move said valving member from one of its pumping positions to the other, and effective to reverse the direction of operation of said motor, at the end of each stroke of said pistons; and m. delay means effective to insure that said limit switches can operate only in an interval between two consecutive jerks. 